Motor vehicle doors are provided with inside door panels, often, but not necessarily, composed of sheet metal, which include access openings to facilitate installation and servicing of parts within the door, as for example door lock mechanisms, window actuators, audio components, etc. Since rain and splash water can ingress to the interior of the door through a number of locations, as for example where the door window emerges from the door interior, it is necessary to seal these openings as between the inside door panel and the interior trim of the door in order to prevent water seepage into the passenger compartment of the motor vehicle. It is, therefore, common practice to adhesively secure a barrier sheet to the door inside panel which sealingly covers one or more of its openings.
The barrier sheets (otherwise known as “water deflectors” or “acoustic barriers”) utilized in the present art are typically a continuous, flexible plastic sheet material having an optical range between clear and opaque, and a material range between a very thin sheet for providing a water barrier to a thick sheet for providing acoustic attenuation and/or vibration damping. Typical materials can include polyethylene, polypropylene, filled polyethylene, modified polypropylene, etc. In some instances, two layers of barrier sheets may be used, for example a first, thinner layer serving to prevent water passage and another, thicker second layer sitting atop the first layer, serving to provide vibration damping and/or acoustic attenuation.
An example of a typical prior art methodology for providing a barrier sheet 10 on an inside panel 12 of a motor vehicle door 14 is depicted at FIGS. 1A through 1D.
At FIGS. 1A through 1C, it will be seen that the inside panel 12 has at least one opening 16 (three openings 16 being shown merely by way of example). The barrier sheet 10 is dimensioned to extend across the openings 16 and to generously overlap onto the generally adjacent, and suitable panel surfaces 12a, as per a predetermined perimeter 18 of the barrier sheet 10. Located within and proximate to the perimeter 18 is disposed a single adhesive bead 20 which locally parallels, more or less, generally the entire perimeter 18. The adhesive bead 20 is sealingly adhered to the inside door panel 12 at one side thereof and an attachment face 10a of the barrier sheet 10 at the diametrically opposite side thereof.
It will be seen, therefore, that if the adhesive seal everywhere has integrity, then water will be sealed from entry into the passenger compartment of the motor vehicle. In order to provide water management, a drain hole 22 is provided at each gravitationally low spot of the adhesive bead 20 (a single drain hole 22 being shown merely by example), whereby water can run along the adhesive bead 20 and then out the drain hole into the door interior and then out the conventional bottom door drain. However, it will be noticed at FIG. 1B, that the adhesive bead 20 must run gravitationally below the drain hole 22, whereby a pocket 24 is present which can retain therein water.
The prior art barrier sheet adhesion process will next be discussed.
Initially the barrier sheet is fabricated, and then placed into an applicator apparatus. The applicator apparatus includes a reservoir for holding a hot melt adhesive which is selectively foamed, as for example by addition of nitrogen gas of between 0% and about 50% to the adhesive (unfoamed adhesive being when nitrogen addition is 0%). The barrier sheet rests upon a table and an applicator head of the applicator apparatus utilizes a nozzle which squeezingly applies a hot melt adhesive bead onto the barrier sheet inside of and proximate to the perimeter thereof. A typical adhesive bead is about 5 mm in diameter.
At an assembly plant, the barrier sheet is aligned with the inside door panel 12 and with the attachment face 10a of the barrier sheet having adhesive bead 20 facing toward the inside door panel, the adhesive bead is pressed against the inside door panel to marry the barrier sheet to the inside door panel. As shown at FIG. 1D, a roller 26 is then rolled along the periphery to cause the adhesive bead along its length to be squeezingly brought into intimate surface-to-surface sealing contact (referred to in the art as “wet-out”) with the inside door panel. The adhesive bead of the barrier sheet is such that when applied to a surface to which it has wet-out contact, the barrier sheet may be peeled off the surface, and the adhesive bead may be again be re-adhered to the surface in a wet-out relation thereto.
Problematically with the adhesion method for barrier sheets in the prior art, an installer has no certain way of knowing (i.e., feedback) whether or not the adhesive bead has achieved fully sealed status (that is, wet-out with the door inside panel) along its entire length, wherein any small void may allow water to leak into the passenger compartment.
Thus, what remains needed in the art is an adhesion methodology for barrier sheets which provides installer feedback as to whether wet-out has been achieved, and further a redundancy of adhesion which provides sealing even if a partial failure of the adhesion occurs.